7

Some telescopes in space have been proposed to function as an interferometer. Being placed several hundreds or thousands of kilometers apart they could actual image exoplanets directly. To my knowledge none of these space telescopes have yet been deployed.
So I was wondering why we don't connect all the several thousand amateur telescopes on Earth together to create a huge interferometer?
That sure would require some efforts (especially software to coordinate it all) but compared to sending telescopes into space it seems outright simple.
Are amateur telescopes simply not strong enough, even when linked together? What would be the best we could achieve?

8192K
  • 173
  • 3
  • 1
    "Linking" in the sense of making an interferometer, is incredibly difficult; it has nothing to do with (say) connecting them on a computer network. As James explains perfectly. – Fattie Oct 30 '16 at 13:21
  • 1
    See also https://astronomy.stackexchange.com/questions/29082/is-optical-vlbi-theoretically-feasible-if-not-why-not – ProfRob Oct 07 '22 at 05:49

1 Answers1

12

You can't make an interferometer by combining photographs. You need to combine the light sources so that the light waves can "interfere", which means you need to have not only the intensity of the light, but also the phase of the wavelength. A CCD only detects the intensity.

You also need to position your telescopes to sub-wavelength accuracy. For Radio telescopes, with long wavelengths, it is possible to detect and then combine the radio signals from several telescopes electronically. That's not possible with light. Visible wavelength interferometers capture the light and combine it as light. It requires very high precision.

Finally, we still have the atmosphere to contend with. Amateur observers know that, beyond a certain size (about 10in), larger telescopes don't have greater resolution, because of the blurring due to the atmosphere1. Bigger mirrors mean more light, mean dimmer objects can be seen, but no more detail is visible. There are ways of getting round this, (Lucky imaging) but these are not suited to interferometery.

So since placing amateur telescopes at nanometer accurate positions, and linking their output with single strand optical fibre is beyond the budget of amateurs, and since the results would be limited by the distortion of the atmosphere, this is not normally done.

1Large observatories like the Very Large Telescope use Adaptive optics to obtain dramatically improved resolution through Earth's atmosphere but that kind of technology is sophisticated and out of reach of amateur instruments.

uhoh
  • 31,151
  • 9
  • 89
  • 293
James K
  • 120,702
  • 5
  • 298
  • 423
  • This is a great answer! I added a footnote just to help some future readers understand why interferometry is perfectly workable for observatories even though it's probably out of reach for amateur instruments. – uhoh Jan 16 '21 at 21:16
  • The VLTI of ESO indeed DOES combine the near-infrared light of the 4 constituent 8m telescopes in order to create a single even larger telescope. So, yes, it is possible. But of course way way beyond what one can do with amateur equipment. – planetmaker Jan 17 '21 at 07:48
  • I wonder if it might be possible to phase lock the frame rate of a video source to the incoming light... – Tripp Kinetics Sep 22 '22 at 17:59
  • @Tripp by the time you make a video, you are recording only the intensity of the light and you have lost the important phase of the light wave information that is needed to do interferometry. – James K Sep 23 '22 at 17:42
  • @JamesK But if you are phase locking the timing of the frames, you can be assured of the relative phase of the frames of the two videos. – Tripp Kinetics Sep 23 '22 at 22:31
  • No! because the videos are taken at different locations. the interference between phases is how interferometry works. – James K Sep 24 '22 at 05:01